Trouble bleeding air

[halleyholmes]

Hi all, new diesel owner here. I replaced the fuel filters on my Yanmar 3YM30 yesterday but when it came time to bleed air from the system, the lift pump wasn't drawing fuel from the tank into the CAV primary filter (I did doublecheck that I'd opened the line from the tank). I understand that using the lift pump is a slow process but after several minutes of pumping, I took the filter off and it was still bone dry. I did open the bleed screw over the secondary filter and the pump was pushing air out of there, so the pump itself doesn't seem to be the issue. It seems like it isn't getting suction due to a bad seal somewhere, but other than the bleed screws themselves I can't imagine where it could be occurring, especially since I'd replaced two missing O-rings when I took the original filter off (the one that sits between the filter and the head and the one that fits onto the central spindle that the filter fits around).

Does anyone have any suggestions? Youtube has been of no help.

 

[alldodge]

Your boat may have a antisiphon valve on the tank fitting. Its a barbed type fitting which has a check ball inside. Can also use a fuel can and just stick the line in the tank to get all filled up

 

[Grub54891]

Had one several years ago that a customer brought in. Took a while but I found a double gasket on a racor filter. Problem solved.

 

[halleyholmes]

Thanks, that was a clever idea! Sadly I didn't go about this on a very scientific manner so I can't say which actually has an effect, but I took your suggestion and put the hose in a small container of fuel so that I could see if the level changed. Having read some discussion on another forum, I also pumped with only the secondary bleed screw open, contrary to what I've understood from various YouTube videos, and am drawing fuel from the cup. Now my next question is, after bleeding air from the secondary screw, do I still need to bleed the primary? I just tried (secondary closed, primary open) but I'm not drawing fuel, nor am I getting any bubbling at the screw.

 

[alldodge]

Don't know if you have to, but all diesels won't run with air in the lines or won't run very long. If there is a bleed screw I bleed it.

 

[QBhoy]

Hi all, new diesel owner here. I replaced the fuel filters on my Yanmar 3YM30 yesterday but when it came time to bleed air from the system, the lift pump wasn't drawing fuel from the tank into the CAV primary filter (I did doublecheck that I'd opened the line from the tank). I understand that using the lift pump is a slow process but after several minutes of pumping, I took the filter off and it was still bone dry. I did open the bleed screw over the secondary filter and the pump was pushing air out of there, so the pump itself doesn't seem to be the issue. It seems like it isn't getting suction due to a bad seal somewhere, but other than the bleed screws themselves I can't imagine where it could be occurring, especially since I'd replaced two missing O-rings when I took the original filter off (the one that sits between the filter and the head and the one that fits onto the central spindle that the filter fits around).

Does anyone have any suggestions? Youtube has been of no help.

Hi. I’m suspecting you have put on seals that shouldn’t be there. Very often new filters come with those seals that go round the spindle thread, but aren’t used in lots of applications. These filters are used widely for all sorts of uses. If you didn’t have them before, don’t fit them just because they are in the box. Take it off and try again. You’re probably not getting a good deal with that on. Best of luck and let me know how you go. They aren’t used on the diesel engines I maintain each year. They get left in the box. I may be wrong…but very common thing for exactly this to be done. Worth checking anyway and that the other seals haven’t been nipped or displaced too.
Otherwise, make sure the primary filter is all sealed and no vent or drain open…open the bleed vent on the secondary filter on engine, and keep pumping. That’s all made much easier if you have filled the primary cav filter with diesel first, of course. Otherwise you’ll be there a while.

 

[Grub54891]

Something I did to myself once: forgot to turn the valve back on at the tank.